This invention relates in general to sample component detection in systems for sample separation and analysis and in particular to detection systems in electrophoretic separation.
Capillary electrophoresis (CE) is a powerful analytical separation technique for the analysis of complex mixtures. In CE, an unknown sample is introduced at an inlet of a capillary channel filled with a buffer solution, and a high voltage is applied across a section of the capillary. Different constituents of the sample migrate through the capillary at different rates depending on their electrophoretic mobilities. Mobility is a complex function of a particle's charge, mass, and shape in solution. A difference in mobilities allows separation of the sample into its components. By detecting the chemicals passing through a part of the capillary or its outlet as a function of time, and knowing the mobilities of the possible constituents, the chemical composition of the sample can be determined.
A number of detectors have been developed for CE, including absorbance, fluorescence, mass-spectrometric and electrochemical methods. Electrochemical detection has certain advantages including sensitivity and selectivity for individual species. Several different types of electrochemical detection can be used, including conductivity measurements, impedance spectroscopy, amperometry and voltammetry. Two key problems with electrochemical detection that need to be overcome are isolation of the detection apparatus from the 1 to 30 kV potential present, and rejection of power supply noise. If the electrodes are not precisely perpendicular to the fluid flow in the separation channel, a large noise signal may be coupled into the electrodes from the high voltage power supply. Another difficulty with previous electrochemical detectors is the irreproducible construction and inaccurate placement of the electrodes inside the separation column. It is therefore desirable to provide an improved detector that overcomes the above-described problems.